1. Field of the Invention
The present invention relates in general to an AC drive type display apparatus and more particularly to an AC drive type display apparatus having a drive circuit for applying a sustaining drive voltage, a turn-on pulse and a turn-off pulse to a matrix type display panel.
2. Description of the Prior Art
A plasma display is a display panel utilizing a gas discharge phenomenon. In the display, a plurality of electrodes are faced through a discharge gap to make picture elements at the cross points, and desirable picture elements corresponding to the picture signal or the original picture are respectively made luminous to display the picture. It has been proposed to provide an AC drive system for the discharge display panel. In the system, an AC sustaining drive voltage is applied to desirable picture elements (usually all of picture elements are in a normal state) and a suitable turn-on pulse is applied to the picture elements which will be made luminous at the time for imparting luminescent dots, and a suitable turn-off pulse is applied to them at the time for extinction.
The AC sustaining drive voltage has a peak (crest) value which is lower than the discharge initiation voltage of the picture elements. When the AC sustaining drive voltage is always applied, it is possible to provide intermittent repeating luminescences during the time from the application of the turn-on pulse to the application of the turn-off pulse. This is referred to as a memory function which is a characteristic of the drive system.
FIG. 1 is a plane view of a display panel of a plasma display; and FIG. 2 is a sectional view taken along the line II-- II of FIG. 1. FIG. 11 is a partial broken schematic view of a display panel. The display panel is generally designated by the reference numeral 1, and includes a lower substrate 10, an upper substrate 20 and a middle substrate 30 therebetween. The lower substrate 10 has a rectangular plate 12 made of a transparent insulator, such as a glass plate. A first group of electrodes (drive lines) 14 are disposed on one surface of the plate 12 and are composed of a plurality of fine electrodes.
The electrodes which are linear are disposed in parallel with substantially equal spaces to each other in a longitudinal direction, as shown in FIG. 1. The first group of electrodes 14 are covered with a transparent insulating plate 16 at all parts except both of the end parts.
The plate 16 can be a glass plate and has a plurality of linear grooves for fitting the electrodes on the surface faced to the plate 12.
The surface 16a (FIG. 2) of the plate 16 opposite to the plate 12 is a flat surface.
The upper substrate 20 has a structure similar to the lower substrate 10, and has a rectangular plate 22 made of a transparent insulator, such as glass. A second group of electrodes (drive lines) 24 are disposed on one surface of the plate and are composed of a plurality of fine electrodes.
The electrodes which are also linear are disposed in parallel with substantially equal spaces to each other in a longitudinal direction as shown in FIG. 1. The second group of electrodes 24 are also covered with a transparent insulating plate 26 such as a glass plate at all parts except both of the end parts. A plurality of linear grooves are provided for fitting the electrodes on the surface faced to the plate 22. The surface 26A (FIG. 2) of the plate 26 opposite to the plate 22 is a flat surface.
The lower substrate 10 and the upper substrate 20 are assembled into the panel with the middle substrate 30 between them, wherein the longitudinal directions of the plates 12 and 22 are orthogonal and the longitudinal directions of the first group of electrodes and the second group of electrodes are orthogonal.
The middle substrate 30 is disposed so as to be bonded to the flat surface 16A of the plate 16 and to the flat surface 26A of the plate 26 so as to form a gap 32.
The surfaces 16A and 26A are disposed in parallel to each other whereby the gap between the surfaces 16A, 26A is substantially equal to any position. The gap 32 is made in a vacuum and then filled with an inert gas, such as neon or argon gas. A plurality of picture elements are made in the gap, at the cross points of the first group of electrodes 14 and the second group of electrodes 24. The first group of electrodes 14 are referred to as X electrodes and the second group of electrodes 24 are referred to as Y electrodes.
FIG. 12 is a block diagram of a control circuit for the display panel 1. The control circuit includes an X drive circuit 30X for the X electrodes 14 and a Y drive circuit 30Y for the Y electrodes 24. The X drive circuit 30X has output terminals E.sub.11 . . . E.sub.ij . . . E.sub.mm, which are equal in number to the X electrodes 14 and are respectively connected to the X electrodes.
The Y drive circuit 30Y has output terminals F.sub.11 . . . F.sub.ij . . . F.sub.nn, which are equal in number to the Y electrodes 24 and are respctively connected to the Y electrode lines.
In FIG. 12, the number of the X electrodes and the number of Y electrodes are respectively nine.
Referring to FIGS. 13a, 13b and 13c, the voltages applied to the display panel 1 and the luminescent operation of the panel 1 resulted by applying the voltages to the display panel 1 by the control circuit will be described.
FIG. 13a shows the voltage applying state for the picture elements and the luminous state which results from applying the voltage. FIG. 13b shows the voltage applying state for applying the voltage from the X drive circuit 30X to the X electrodes. FIG. 13c shows the voltage applying state for applying the voltage from the Y drive circuit 30Y to the Y electrodes. In FIGS. 13a, 13b and 13c the reference V.sub.s designates the AC sustaining drive voltge which is applied to all of the picture elements;
V.sub.sx designates the sustaining drive voltage applied to the X electrodes;
V.sub.sy designates the sustaining drive voltage applied to the Y electrodes;
V.sub.p designates the turn-on pulse;
V.sub.px designates the turn-on pulse applied to the X electrodes;
V.sub.py designates the turn-on pulse applied to the Y electrodes;
V.sub.q designates the turn-off pulse;
V.sub.qx designates the turn-off pulse applied to the X electrodes;
V.sub.qy designates the turn-off pulse applied to the Y electrodes;
.+-. V.sub.f designates the discharge initiation voltage of each picture element and L designates luminescence.
The sustaining drive voltages V.sub.sx, V.sub.sy have equal repeating periods and pulse widths to each other, and have a phase difference so that one pulse is generated at the middle of the quiescent time of the other pulse. The peak value of the sustaining drive voltage is selected to be lower than the discharge initiation voltage .+-. V.sub.f. The voltage V.sub.sx is applied to all of the X electrodes and the voltage V.sub.sy is applied to all of the Y electrodes. The voltages V.sub.sx, V.sub.sy provide a positive polarity to the X electrodes and the Y electrodes. The turn-on pulses V.sub.px, V.sub.py are simultaneously applied to the picture elements which will be luminous in opposite polarity to each other. The peak values of the turn-on pulses V.sub.px, V.sub.py are respectively one half of the peak value of the turn-on pulse V.sub.p. The turn-off pulses V.sub.qx, V.sub.qy are also simultaneously applied to the picture elements in opposite polarity to each other. The peak values of the turn-off pulses V.sub.qx, V.sub. qy are respectively one-half of the peak value of the turn-off pulses V.sub.q. The peak value of the turn-off pulse V.sub.q is lower than the sustaining drive voltage V.sub.sx.
Referring to FIGS. 13a, 13b and 13c, the operation of the display panel of FIG. 1 will now be explained. In order to drive the display panel, the AC sustaining drive voltage V.sub.s of FIG. 13a is always applied across the discharge gap 32 of the picture elements through the X electrodes and the Y electrodes, and when the turn-on of certain picture elements is required, a discharge occurs for the picture elements by applying the turn-on pulse V.sub.p which provides a level which is higher than the discharge initiation voltage V.sub.f.
Once the discharge has occurred, the luminescence L is intermittently given until the turn-off pulse V.sub.q of FIG. 13a is applied.
FIG. 3 is a diagram illustrating one embodiment of the drive circuit for a display panel of the conventional AC drive discharge type display apparatus, wherein V.sub.s designates a sustaining drive voltage terminal; V.sub.p designates a turn-on voltage terminal; S.sub.ai (i = 1,2,3) S.sub.bj (j -- 1,2,3) designate selective switch circuits; and E.sub.ij (i, j = 1,2,3) designate output terminals. The drive circuit is a matrix type circuit wherein AND circuits are formed by the resistances and the diodes. In FIG. 3, nine lines of the liner electrodes 14 (FIG. 1) are provided as the X electrodes of the display panel and the output terminals E.sub.ij are connected to one linear electrode 14 of the X electrodes of the display panel, and therefore the linear electrodes 14 are connected through the output terminals E.sub.ij, to three circuit elements which consist of two diodes D.sub.a, D.sub.b and one resistance R.sub.a.
In the drive circuit, the sustaining drive voltage V.sub.s having the waveform of FIG. 13b, is applied as an input to the sustaining drive voltage terminal V.sub.s, is passed through the diode D.sub.a to the output terminal E.sub.ij for the X electrode, and then is passed through the diode D.sub.b and a selective switch circuit S.sub.bj of a switch element, e.g., a transistor which is usually in the ON state, to the sustaining drive voltage terminal V.sub.s. In order to apply the turn-on pulse shown in FIG. 13b, one switch of the first selective switch circuit S.sub.ai which is connected to the turn-on voltage terminal V.sub.p, is turned on and one switch of the second selective switch circuit S.sub.bj is turned off, whereby the turn-on pulse V.sub.p is applied through one terminal of the output terminal E.sub.ij to one linear electrode 14 of the X electrodes of the display panel. For example, when the turn-on pulse V.sub.px is applied to the X electrodes which is connected to the output terminal E.sub.22, the switch S.sub.a2 is turned on and the switch S.sub.b2 is turned off, whereby the current is passed through three transverse resistances R.sub.a connected to the switch S.sub.a2. However, since the switches S.sub.b1 and S.sub.b2 are in the ON state, the current passing through the vertical lines is passed through the diode D.sub.b and the switches S.sub.b1, S.sub.b3 to the sustaining drive voltage terminal V.sub.s, and accordingly the turn-on pulse V.sub.px is not applied to the X electrodes connected to the output terminals E.sub.21, E.sub.23, and the turn-on pulse V.sub.px is applied only to the X electrode connected to the output terminal E.sub.22 in the line of the switch S.sub.b2 which is in the OFF state. The selectivity is a characteristic of the AND circuit which consists of the resistance and the diode. The turn-off pulse V.sub.qx (FIG. 13b) can also be applied separately to each of the linear electrodes of the X electrode in a manner similar to the case of the turn-on pulse V.sub.px.
While somewhat satisfactory, the conventional drive circuit for the display panel using the AND circuit system of the resistance and the diode disadvantageously requires a large consumption of power since an unnecessary current is passed through the resistance R.sub.a to the circuit connected to the linear electrodes 14 to which the turn-on pulse and the turn-off pulse are not applied.
The conventional drive circuit also disadvantageously requires three circuit elements consisting of two diodes D.sub.a, D.sub.b and one resistance R.sub.a for each linear electrode 14, and accordingly the number of circuit elements is large.